K.G. Vandervoort

Is gas-discharge plasma a new solution to the old problem of biofilm inactivation?

Conventional disinfection and sterilization methods are often ineffective with biofilms, which are ubiquitous, hard-to-destroy microbial communities embedded in a matrix mostly composed of exopolysaccharides. The use of gas-discharge plasmas represents an alternative method, since plasmas contain a mixture of charged particles, chemically reactive species and UV radiation, whose decontamination potential for free-living, planktonic micro-organisms is well established. In this study, biofilms were produced using Chromobacterium violaceum, a Gram-negative bacterium present in soil and water and used in this study as a model organism. Biofilms were subjected to an atmospheric pressure plasma jet for different exposure times. Our results show that 99.6 % of culturable cells are inactivated after a 5 min treatment. The survivor curve shows double-slope kinetics with a rapid initial decline in c.f.u. ml(-1) followed by a much slower decline with D values that are longer than those for the inactivation of planktonic organisms, suggesting a more complex inactivation mechanism for biofilms. DNA and ATP determinations together with atomic force microscopy and fluorescence microscopy show that non-culturable cells are still alive after short plasma exposure times. These results indicate the potential of plasma for biofilm inactivation and suggest that cells go through a sequential set of physiological and morphological changes before inactivation.

Magnetization hysteresis and flux pinning in twinned and untwinned YBa2Cu3O7−δ single crystals

Measurements of the magnetization hysteresis of the same crystal in the twinned and untwinned state reveal that pinning due to twinning planes may contribute a substantial, anisotropic fraction of the observed critical currents. A linear scaling between magnetization hysteresis and sample dimension shows that the twinned and untwinned crystal does not exhibit any subgranular effects.

Origin of enhanced growth of the 110 K superconducting phase by Pb doping in the Bi‐Sr‐Ca‐Cu‐O system

Kinetics of the 110 K superconducting phase formation has been studied in the Bi‐Sr‐Ca‐Cu‐O system with and without the addition of small amounts of lead. The kinetics of the phase transformation has been greatly affected by lead doping. The time required for the maximum formation of the 110 K phase is substantially reduced by the addition of lead. This phenomenon has been shown to be associated with the lead enhancing the nucleation and growth process of the 110 K phase and the diffusivity of calcium and copper.

120 K superconductivity in the (Bi, Pb)-Sr-Ca-Cu-O system

Abstract Superconductivity with onset at 120 K and zero electrical resistance at 105 K is observed in the system (Bi, Pb)-Sr-Ca-Cu-O with the composition Bi 0.7 Pb 0.3 Sr 1 Ca 1 Cu 1.8 Oδ. The transition temperature and room temperature resistivity of the samples depend on the rate of cooling from the sintering temperature. We report the synthesis, superconducting temperature, and X-ray diffraction measurements of the above compound.

Full temperature calibration from 4 to 300 K of the voltage response of piezoelectric tube scanner PZT‐5A for use in scanning tunneling microscopes

We have calibrated the displacement/voltage (A/V) response of our piezoelectric scanning tube (PZT‐5A) by imaging graphite at over 40 temperatures between 4 and 300 K. We have also calibrated the (A/V) response as a function of voltage up to 220 V at room temperature, imaging a gold‐plated diffraction grating. We find that the temperature dependence of the (A/V) response is linear to within 10% and is reduced by a factor of 5.5 on decreasing temperature from 300 to 4.2 K. The near linearity with temperature of the (A/V) response makes the PZT‐5A lead zirconate titanate composition a convenient choice for low temperature scanning tunneling microscope piezo tube elements.

The upper critical field of Ba1−xKxBiO3

Abstract Resistive measurements in magnetic fields up to 8 T and at temperatures between 0.5 and 150 K for Ba 1− x K x BiO 3 polycrystalline samples with various values of x are presented. Low-field magnetic measurements indicate bulk superconductivity for all concentrations measured with T c ranging from 25.6 K to 28 K for x ranging from 0.35 to 0.45. The upper critical field as a function of concentration and temperature is determined from the resistive measurements. A lower limit of 40 A is derived for the superconductive coherence length. There is a negative magnetoresistance in the normal state at low temperatures. The resistive transition curves depend strongly on the measuring current. We propose a granular model of superconductivity to explain this and other unsual features of the data.

110 k superconductivity in crystallized Bi-Sr-Ca-Cu-O glasses

Abstract Superconducting transition temperatures near 110 K are observed in the Bi-Sr-Ca-Cu-O system with the nominal compositions Bi 2 Sr 2 Ca 3 Cu 4 O x and Bi 2 Sr 2 Ca 4 Cu 5 O x . Electrical resistivity, magnetization, and X-ray diffraction data are reported. Also discussed is the effect of heat treatment on the thermodynamic behavior of the superconducting phases in the rapidly quenched glasses.

Photoelectron spectroscopy study of YBa2Cu3Ox with varied oxygen stoichiometry: Possible evidence for strong coupling superconductivity

Photoelectron spectroscopy measurements are reported for samples of YBa2Cu3Ox with oxygen content varied in the range 6.2<x<6.9. For the most oxygen rich samples, a prominent cutoff at the Fermi edge is observed. The electronic density of states at the Fermi level N(EF) falls as oxygen is depleted. The superconducting transition temperature TcαtN(EF) suggest ing that a strong coupling mechanism controls the superconductivity.

Pseudomonas aeruginosa Biofilm Inactivation: Decreased Cell Culturability, Adhesiveness to Surfaces, and Biofilm Thickness Upon High-Pressure Nonthermal Plasma Treatment

Bacterial biofilms are more resilient to standard killing methods than free-living bacteria. Pseudomonas aeruginosa PAO1 biofilms grown on borosilicate coupons were treated with gas-discharge plasma for various exposure times. Almost 100% of the cells were inactivated after a 5-min plasma exposure. Atomic force microscopy was used to image the biofilms and study their micromechanical properties. Results show that the adhesiveness to borosilicate and the thickness of the Pseudomonas biofilms are reduced upon plasma treatment.

Evidence from photoemission of strongly hybridized states at the Fermi level of Bi2Sr2CaCu2O8

The nature of the states at the Fermi level of the high temperature superconductors is of crucial importance since it is these states which form Cooper pairs below T c which are responsible for the superconductivity. In particular it is important to discern whether these states are derived from the Cu 3d or O 2p orbitals. Recent resonant photoemission experiments claim that there is no Cu 3d character at the Fermi edge of the Bi 2 Sr 2 CaCu 2 O 8 materials. While we observe similar resonant effects in these materials, an investigation over a wide range of photon energies, hv = 15 to 100 eV, has led us to reevaluate these results and to conclude that there is comparable O 2p and Cu 3d character at the Fermi edge. Our findings give support to strongly hybridized one band or two band descriptions of these materials.